The present invention relates to a projection type color picture display system, and in particular to a projection type color picture display system for reproducing color television broadcast pictures, information including pictures recorded on a video camera or a VTR and for displaying the information thus reproduced on a large screen.
As an example of the projection type color picture display system, a projection type color television picture display system is shown in FIGS. 1A and 1B. FIG. 1A schematically shows the structure of the system. FIG. 1B schematically shows the optical arrangement of the optical system and the screen of the color television picture display system.
In a projection type color picture display system, the highly bright picture formed on the phosphor screens of cathode-ray tubes CRT.sub.1 to CRT.sub.3 is enlargedly projected onto a screen (a transmission type screen having a Fresnel lens FL, for example) S via an optical system including projection lenses L.sub.1 to L.sub.3 and reflex mirrors M.sub.1 and M.sub.2. In a projection type cathode-ray tube used in this system, therefore, the phosphor screen is loaded with electron beam energy, which is not less than ten times that of a conventional picture tube, i.e., a direct-view cathode-ray tube, in order to enhance the brightness on the screen S as much as possible. When a white pattern is reproduced on the projection screen, approximately 70% of the brightness is occupied by the green color.
In green picture producing cathode-ray tubes used in conventional projection type color picture display system, a phosphor material of manganese activated zinc silicate (Zn.sub.2 SiO.sub.4 :Mn) phosphor material producing a high color purity, a phosphor material of terbium activated gadolinium oxysulfide (a Gd.sub.2 O.sub.2 S:Tb phosphor material), a phosphor material of terbium activated yttrium silicate (a Y.sub.2 SiO.sub.5 :Tb phosphor material), a phosphor material of terbium activated yttrium aluminate (a Y.sub.2 A1.sub.5 O.sub.12 :Tb phosphor material), a mixed phosphor material composed of the phosphor material of yttrium aluminate and the above described phosphor material of manganese activated zinc silicate or the like were used. However, the phosphor material of manganese activated zinc silicate is not suitable for practical use since it causes long persistence and deterioration of the brightness due to the electron beam. Further, various terbium-activated phosphor materials have drawbacks of poor color purity although they are generally used for projection type cathode-ray tubes as described in Technical Report published by the Institute of Television Engineers of Japan, March 18, 1982, pp. 13-17, IPD 66-3, for example.
The projection type color picture display system composed of a cathode-ray tube (CRT) using such a green light emitting phosphor having a poor color purity is not only poor in green color purity but also unadvantageously narrow in color reproduction range of picture.